1911] Notes on the Pear-Slug 183 



Parthenogensis probably occurs with this insect, but this has 

 not been satisfactorily proved. Many sawflies were examined, 

 but no males were found. Eggs deposited by virgin females 

 hatched, but all the larvae were weak, and none even reached the 

 second stage. 



The Larva. The newly hatched slug is about 1.2 mm. long, 

 at first free from slime, but this is secreted in a few hours. The 

 young slugs begin to eat out tiny patches in the epidermis; 

 later they eat through the parenchyma to the lower epidermis, 

 leaving the veins. One slug ate a space of 825.9 square milli- 

 meters during its lifetime, 19 days, according to a record kept 

 by Mr. T. M. McCall, insectary assistant at the time. 



After each molt, except the last, the larvae eat their cast 

 skin, all of it but the head. 



Five molts are probably normal. In 14 cases 5 larvae 

 molted 5 times; 5, 6 times; 3, 7 times, and 1 larva molted <S 

 times, all under insectary conditions. Sometimes in succes- 

 sive molts the width of the cast head was exactly the same; 

 often there was very little difference. 



The average head widths of the stages were: Stage I, 

 .35 mm.; II, .51 mm.; Ill, .67 mm.; IV, .85 mm.; V, 1.04 mm.; 

 VI, 1.13 mm. The geometrical ratio between the successive 

 head widths was practically .35. 



Larvae matured in 13 to 2G days; average 19.4 days. No 

 essential differences were noticed in the two generations of the 

 time required; the same total length was found in either case. 

 The time required for the separate stages was: I, 5 days; II, 

 3.2 days; III, 3.4 days; IV, 3.2 days; V, 4.7 days (average from 

 both generations). Stage VI usually entered the soil imme- 

 diately after molting. 



Both Peck and Marlatt remarked that heavy rains are said 

 to destroy the slugs. Professor Peck, however, said that he had 

 seen the slugs retreat to the under sides of the leaves in a shower; 

 a fact that we observed several times in the Iowa work. It 

 seems quite likely that the supposed efficiency of heavy rains 

 is really only the disappearance of the slugs to the lower sides 

 of the leaves. 



How the larvae reached the ground was a puzzle to us at 

 first, but we found that they dropped down of their own accord. 

 Occasionally orange-colored larvae were found on tree trunks, but 

 they were not crawling down, but appeared to be going upward. 



